The polycondensation or polymerization of low molecular weight siloxanol oils has been practiced for several years. A wide range of catalysts have been used to perform these processes with reasonable reaction time and temperature. Catalysts that can be used include sulfuric acid, trifluorosulfonic acid, some Lewis acids, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, tetrabutylphosphonium silanolate and some amines. (See, for example, (a) "The Siloxane Bond" Ed. Voronkov, M. G.; Mileshkevich, V. P.; Yuzhelevskii, Yu. A. Consultant Bureau, New York and London, 1978; and (b) Noll, W. "Chemistry and Technology of Silicones", Academia Press, New York, (1968)). A number of patents disclose the preparation and use of linear phosphonitrilic chlorides as catalysts for polycondensation and redistribution of the low viscosity siloxane polymers. In particular, U.S. Pat. No. 2,830,967 (1958), U.S. Pat. No. 3,186,967 (1965), U.S. Pat. No. 3,839,388 (1974), U.S. Pat. No. 4,725,643 (1988), U.S. Pat. No. 4,975,510 (1990) (to Wacker Chemie) disclose that linear phosphonitrilic chlorides represented by formula Cl.sub.3 P(NPCl.sub.2).sub.n NPCl.sub.3.sup.+ PCl.sub. 6.sup.-, wherein n is an integer of from 1 to 6, preferably 1, are effective as catalysts for polycondensation and equilibration of the low viscosity siloxane polymers. These catalysts are especially valuable for the production of silicone rubber and siloxane fluids with a low content of hydroxyl end groups. More recently, U.S. Pat. Nos. 4,888,405 and 5,008,229 (1991) (to Wacker Chemie) have disclosed new catalytic compositions containing phosphonitrile chlorides and/or reaction products of phosphonitrile chlorides with organopolysiloxanes and/or organosilanes, the latter also including a solubilizer and a halogen-free solvent. A recent patent (GB Patent 2,252,969 (1992)) (to Dow Corning) describes catalyst compounds of general formula: Cl.sub.3 P(NPCl.sub.2).sub.n NPCl.sub.3.sup.+ ECl.sub.m.sup.- where E is an element having an electronegativity value of from 1.2 to 2 such as Al, Sb, P, Sn, Zn and Fe.
In spite of the foregoing developments, there is a continuing search for catalysts which will improve activity in the polymerization of organosiloxanes. It is known that the application of standard linear phosphonitrilic chlorides (LPNC's) as catalysts for polycondensation of low molecular siloxanediols can produce a high molecular gum which does not contain cyclic oligosiloxanes and that the gum can be prepared in a short cycle time. The present work has shown that the physical mixture of high molecular weight organopolysiloxanes and low molecular weight siloxanes can be redistributed into linear polymers, which have an average number molecular weight, without formation of a significant amount of cyclic species. In addition, it has been discovered that compositions containing novel reaction products of linear phosphonitrile chlorides with compounds containing active protons with pKa values below 18 are active catalysts for polycondensation and redistribution of organosiloxane polymers. In particular, it has been found, for example, that novel products of reaction of 1 mol of LPNC of formula EQU Cl.sub.3 P(NPCl.sub.2).sub.n NPCl.sub.3 . PCl.sub.6
with preferably 1 to 4 mols, of compounds containing active protons with pKa values below 18 yields very active catalysts for polycondensation and rearrangement of organosiloxanes. The solvents and low boiling products were removed from the system by vacuum at 80.degree. C. over a period of 2 hours. The resulting light yellow residue is soluble in many organic solvents such as methylene chloride, methanol, ethers and low viscosity silicone oil. The chlorine analysis showed that this new composition contains significantly lower amounts of chlorine than the starting LPNC. The new chemical compositions described above were also tested as a catalyst for polycondensation and redistribution of organosiloxanes. The catalytic activity of this new catalyst was higher than the standard LCPN. The products of the polycondensation and redistribution of organosiloxane polymers do not contain oligomeric cyclic species. The development and use of such standard and new and improved catalysts for polycondensation and redistribution of organosiloxanes is the subject matter of the present invention.